Reactive packing for metallurgical refractories



Patented Dec. 24, 1929 UNITED STATES PATENT OFFICE CHARLES SAMUELHOLLAND'ER, F YHILADELPHIA, AND EDWARD LESLIE HELWIG, OF BRISTOL,.PENNSYLVANIA REACTIVE PACKING FOR METALLURGICAL REFRACTORIES NoDrawing.

In the operation of electric furnaces a crack in the refractory wall isalways a source of danger. This is especially true if the chargeconsists of molten or boiling metal as the flow of material through arefractory break'would immediately endanger any resistors or inductorsused to produce the heating effect. It would consequently be a decidedadvancement in the state of the art to be able to seal up such cracks asthey are formed and thus prevent the charge from escaping. This wepropose to do by backing the crucible or retort with a layer ofgranular, powdered or sintered material containing a constituent whichwill, at

the temperatureencountered, react with the material of the charge toform a product whichis solid or plastic at the prevailing temperature.In case of a crack then the molten or vaporized charge will immediatelyencounter this reactive material and the products of the reaction willblock its flow.

\Ve are aware that, in the past, crucibles and retorts have been coatedon the outside with materials to prevent the flames or gases of a,combustion furnace from attacking the body of the refractory. Graphitecrucibles, for instance, have been given a siliceous outer coating forthis purpose. However this is totally different from the purpose of ourinvention.

It has also beengeneral practice in the past to back the crucibles ininduction furnaces with a granular refractory for the purpose ofsupporting the crucibles. In the event of a break, this wouldmechanically absorb a certain amount of the charge in its pore space butwould not necessarily react with it to form a repair. Since it does notreact, there is a great danger of the unreacted charge chemically at- 0tacking the coils or short circuiting them.

Example 1.- A clay-graphite crucible is sawed in half and the saw cutscarred with a file. This is to imitate a cracked crucible. It is,placed inside a larger clay-graphite crucible and the space between themis packed tightly with a mixture of four parts finely ground silica andone part monobasic sodium phosphate. The inner crucible is filled withmetallic zinc. The whole assembly is placed in an electric resistancefurnace and heated Application filed February 6, 1929. Serial No.338,021.

until the zinc boils vigorously. It is then cooled, taken apart andexamined. It is found that the zinc has filled the file marks in the sawcut and has begun to leak through into the packing. No metallic zinc isfound in the packing however. Instead, a half inch, hemispherical zoneof sintered material is found at the end of each file mark which showsthe extent to which the reaction has penetrated. The crack iseffectively sealed and the charge retained inside the broken crucible.

'The experiment is repeated, substituting silica powder alone for themixture described above. At the end of the experiment the bulk of thecharge is found in the bottom of the outer crucible and zinc is founddisseminated throughout the packing. No reaction occurs in this casewhile in the former experiment a true chemical reaction occurs betweenthe 7 packing and the charge.

Example 2.A clay-graphite retort containing zinc is surrounded by aninductor coil. The space between the crucible and the coil is tightlypacked with a mixture of one part acid sodium phosphate and four partsfinely ground silica. The zinc is brought to boiling by ower applied tothe inductor coil. In the event of a break in the crucible, the zincvapor or molten zinc, as it emerges from the retort, immediately reactswith the constituents of the packing forming a plastic material whichprevents a further flow of metal from the break.

Example 3.-The clay-graphite crucible used in Example 1 is charged withiron sulphide and it is surrounded with a tightly packed layer of amixture of three parts silica powder and one part sodium carbonate. Itis heated well above the melting point of the iron sulphide, then cooledand examined. The charge has been retained inside the broken crucibleand the cracks effectively sealed.

These examples are merely given by way of illustration and should not betaken as limiting us in the application of this principle. It is onlylimited to the use of such materials as will react with the charge atthe prevailing temperature and is applicable to all types of 100furnaces where a packing may be used to surround the charge container.

\Ve claim as our invention 1. The process of blocking egress of a chargein case of a refractory failure of a crucible or retort by surroundingthe crucible or retort with a packing which will react chemically withthe contents to form a plastic mass at the prevailing temperature.

2. The process of blocking egress of a charge in case of a refractoryfailure of a crucible 0r retort by surrounding the crucible or retortwith a packing composed of amixture of silica and an alkali salt whichwill react chemically with the contents to form a plastic mass at theprevailing temperature.

Dr. CHARLES SAMUEL HOLLANDER. EDWARD LESLIE HELWIG.

